^a Defined by the following groups: neurologic and developmental conditions (attention deficit hyperactivity disorder, autism spectrum disorder, cerebral palsy, cognitive dysfunction, muscular dystrophy, neural tube defect or spina bifida, neurologic or neurodevelopmental disorder, neuropathy, plegias or paralysis, preterm birth [for children aged <2 y only], seizure disorder, and wheelchair or walker-dependence or bed-bound status); respiratory conditions (active tuberculosis, asthma or reactive airway disease, chronic hypoxemic respiratory failure with oxygen or ventilator dependence, cystic fibrosis, current smoking or e-cigarette use, tracheostomy dependence, and other chronic lung diseases); cardiovascular conditions (congenital heart disease, valvular heart disease, hypertension, and other cardiovascular disease); metabolic and endocrine conditions (dyslipidemia, obesity, thyroid disorder, type 1 diabetes, type 2 diabetes, and other endocrine disorders); gastrointestinal or hepatic conditions (Crohn’s disease, feeding tube dependence, liver disease, malnutrition, ulcerative colitis, and other gastrointestinal disorders); and psychiatric conditions (anxiety, borderline personality disorder, depression, substance use disorder, and other psychiatric diagnoses).

^b List is not exhaustive but includes the top 3 diagnoses for each age category.

^c Fully vaccinated was defined as having received 2 doses of a messenger RNA–based COVID-19 vaccine at least 14 d before hospital admission date. Partially vaccinated was defined as having received only 1 dose of a messenger RNA–based COVID-19 vaccine at least 14 d before hospitalization. All vaccinated patients in this study received the Pfizer-BioNTech (BNT162b2) vaccine.